Integrator Wind-Up Effect of Recirculation Flow Control System During Large Load Demand Change for Lungmen ABWR Plant

The transient of Large Load Demand Change imposed on the Master Controller of the Recirculation Flow Control System is studied in this paper. The simulation performed in this study used the Core Design and Safety Analysis Package, which includes a lattice calculation code, CASMO-4, a three-dimensional core simulation code, SIMULATE-3, an interface code, SLICK, and a thermal hydraulic code, RETRAN. In the analysis the initial condition of 100% rated power/85% rated core flow was selected as base case, and the load demand was first manually ramped down from 100% to 75% (25% change) at the rate of 1%/sec and then ramped up at the same rate to the original level 150 seconds later. This paper presents the wind-up phenomenon observed in the output of the Proportional Integral (P/I) element when a large load demand change is imposed on the Master Controller of the RFCS. This wind-up phenomenon will cause an unnecessary time delay in response to the change to restore the Master Controller output to above the effective level. The sensitivity studies were conducted to get more insight into the wind-up phenomenon, which included: (1) load demand change of 20% level, (2) different initial core flow, and (3) different gain setting of P/I Controller. The analysis results show that the wind-up phenomenon can be avoided for the load demand change less than 20% or the higher initial core flow than 85% rated. Furthermore, the base setting of the P/I element of the Master Controller is appropriate to prevent the neutron flux from exceeding the scram setpoint with at least 10% margin during the ramp-up stage of load demand change.